1. Field of the Invention
The present invention relates to a method for testing a head element of a thin-film magnetic head and a method for manufacturing a thin-film magnetic head and a head gimbal assembly (HGA), using the testing method. The present invention also relates to a magnetic recording and reproducing apparatus capable of evaluating a thin-film magnetic head.
2. Description of the Related Art
Most of the thin-film magnetic heads currently provided in magnetic recording and reproducing apparatuses such as magnetic disk drive apparatuses and magnetic tape drive apparatuses use a highly sensitive magnetoresistive (MR) effect element having an output that does not depend on the relative velocity to a magnetic recording medium to read data signals from a magnetic recording medium such as a magnetic disk or a magnetic tape.
A problem with such conventional MR effect elements is that defective products that generate Barkhausen noise in their outputs are produced. The Barkhausen noise is generated primarily because a magnetic domain wall is caught in defects in the magnetic film constituting the MR effect element as the magnetic domain wall moves, and is affected substantially by stress applied to the MR effect element. In practice, when an external or internal stress that exceeds a certain amount is applied, inverse magnetostriction disperses the magnetization in the MR effect element to destabilize the structure of the magnetic domains, making it more likely to cause Barkhausen noise. Such a stress can be caused by a distortion of the structure of the element itself as well as increase of deformation by the thermal expansion associated with an increase in the temperature of the element.
The influence of temperature and stress has become more remarkable than ever before especially in recent current-in-plane (CIP) giant magnetoresistive (GMR) effect elements, current-perpendicular-to-plane (CPP) GMR effect elements, or tunnel magnetoresistive (TMR) effect elements, which sense signal magnetic fields with extremely high sensitivities.
Furthermore, in order to stably control the flying height of a thin-film magnetic head, which is set to an ultra-small value in a recent magnetic disk drive apparatus, a technique has come into adoption in which a heating element is provided within a thin-film magnetic head and the end of the head element is caused to be protruded in the direction of the magnetic disk by the heat generated by the heating element to adjust the flying height (see, for example, U.S. Pat. No. 5,991,113). With this technique, thermal asperities and crashes are avoided to maintain good read and write characteristics. However, heat generated by such a heating element further heats the MR effect element and portions around the MR effect element, and can further increase the influence of the temperature and stress.
Approaches to preventing the Barkhausen noise in MR effect elements have been proposed. For example, Japanese Patent Publication No. 2002-133621A proposes a method for determining whether an MR effect element is acceptable or defective by measuring noise generated in response to various values of sense currents flowing through an MR effect element. Japanese Patent Publication No. 06-84116A discloses a technique that gradually increases a sense current passed through an MR effect head to prevent the formation of a magnetic domain structure that is likely to generate noise due to a stress caused by a rapid change in temperature.
However, it has been very difficult to identify heads having the noise problem beforehand with the related art described above.
In practice, it is difficult to prevent stress that can cause noise for reasons of thin-film magnetic head manufacturing technique. Therefore, testing of thin-film magnetic heads must be performed to determine whether a thin-film magnetic head is acceptable or not with respect to noise being output from an MR effect element. Even if a head was tested by using a sense current to cause an MR effect element itself to generate heat to induce thermal stress as in the techniques disclosed in Japanese Patent Publications Nos. 2002-133621A and 06-84116A and was determined as non-defective heads, the head has sometimes caused Barkhausen noise under actual high-temperature conditions.
Furthermore, increasing the sense current value in order to test a head can cause an irreversible change in the MR effect element and make the testing a destructive test. This causes a serious problem especially in the case of a TMR effect element including a tunnel barrier layer, which is an ultra-thin insulating film.